1. Field of the Invention
The present invention relates to a transmission for a vehicle, and more particularly, to a transmission of the type where a single pinion type planetary gear mechanism and a double pinion type planetary gear mechanism are combined in various manners by clutches and brakes to provide five forward speed stages and a reverse stage.
2. Description of the Prior art
When the transmission for a vehicle can provide a larger number of speed stages with correspondingly smaller gear ratios between each two adjacent speed stages, the rotational speed difference between the pump impeller and the turbine runner of the torque converter generally combined with the transmission is kept smaller during the speed shifting, and therefore, the efficiency of the torque converter, and accordingly the fuel economy of the vehicle, will be correspondingly improved, while the speed shift operation of the transmission will be more smoothly performed. Further, a wider variety of transmission ratios is also desirable for better performance of the engine.
In view of these it was a trend in the recent developments of the transmissions for vehicles to provide a larger number of speed stages.
The transmissions for vehicles designed to provide five forward speed stages and a reverse stage are proposed in Japanese Patent Publication 48-27863 (1973) (a combination of a double pinion type planetary gear mechanism and a Ravingeau type planetary gear mechanism), Japanese Patent Publication 50-32913 (1975) (a combination of three single pinion type planetary gear mechanisms), Japanese Patent Laying-open Publication 61-130649 (1986) (a combination of a single pinion type planetary gear mechanism and a double pinion type planetary gear mechanism) and Japanese Utility Model Laying-open Publications 61-117950 (1986) (also a combination of a single pinion type planetary gear mechanism and a double pinion type planetary gear mechanism).
In order for those transmissions providing five speed stages and a reverse stage to operate with good exhibition of the improved performance to be available by such a large number of transmission ratios, it is essential, as an aspect, that the changing over operation of the transmission between the speed stages, i.e. the engagement or disengagement of friction engaging means such as clutches and brakes are precisely controlled by maintaining some delicate timing relations with one another, because otherwise the transmission would be temporarily locked up by an overlapped engagement of two clutches and/or brakes thereby causing an unpleasant shock in the vehicle, or, on the contrary, the transmission would be temporarily released by an overlapped disengagement of two clutches and/or brakes thereby causing also unpleasant revving up of the engine, and, as another aspect, that the transmission is devised to provide a relatively small gear ratio between each two adjacent speed stages, because, although it is desirable that the transmission provides a larger number of speed stages, the overall gear ratio, i.e. the ratio between the lowest speed gear ratio and the highest speed gear ratio need not be increased.